Human intervertebral discs generally serve two functions, they cushion and allow movement between pairs of vertebrae. Cushioning is performed by a gel-like material, which forms the inner part of the discs. A fibrous outer layer surrounds the inner gel-like material. Discs are subjected to a great many strains and stresses and are known to deteriorate with age, injury, or disease. When discs are damaged or diseased, the mobility of the subject is often impaired and great pain may result from movement. Damaged discs may also place pressure on the spinal column, causing pain.